The invention relates generally to semiconductor devices and integrated circuit fabrication and, in particular, to fabrication methods and device structures for a bipolar junction transistor.
Bipolar junction transistors may be found, among other end uses, in high-frequency and high-power applications. In particular, bipolar junction transistors may find use in power amplifiers for wireless communications systems and in mobile devices. Bipolar junction transistors may also be used in high-speed logic circuits. Bipolar junction transistors are three-terminal electronic devices that include semiconductor regions defining an emitter, an intrinsic base, and a collector. An NPN bipolar junction transistor includes n-type semiconductor material regions constituting the emitter and collector, and a region of p-type semiconductor material constituting the intrinsic base situated between the n-type semiconductor material regions. By contrast, a PNP bipolar junction transistor includes p-type semiconductor material regions of constituting the emitter and collector, and a region of n-type semiconductor material constituting the intrinsic base situated between the p-type semiconductor material regions. The emitter, intrinsic base, and collector define a collector-base junction and an emitter-base junction across which the conductivity type of the respective semiconductor materials changes. A voltage applied across the emitter-base junction controls the movement of charge carriers that produces charge flow between the collector and emitter.
Improved fabrication methods and device structures are needed for a bipolar junction transistor.